Marriage is more beneficial for a woman knocking almost two years off her age (and if she moves up the social ladder she can look four years younger – and the same applies to men).

For men marriage generally only knocks off one year but having one to three children makes a man look a year younger while it makes no difference to a woman.

These benefits disappear in families with four children.

Looking chubbier as you get older helps men look younger as it smooths out the wrinkles. Adding 2 points to your body mass index (bmi) will take off a year whereas a woman would have to add 7 points to her bmi to get the same effect.

An affluent married man with no more than three children will look ten years younger than someone who is homeless, single and has lost weight (2 points off his bmi).

All the factors combined can lead to people in their 40s looking up to seven years younger than their contemporaries.

Public Health scientists at the Danish twin registry led the study published in the journal Age and Ageing.

They asked nurses to guess the ages of almost 2,000 identical and non-identical twins in their seventies. They then looked at environmental factors including marriage, parenthood and social class. Previous studies have shown that non-genetic factors account for 40% of the variation in perceived age.

The effects of heavy smoking are relatively modest. You would have to smoke 20 a day for 20 years to gain extra wrinkles and tobacco smoke only causes half that damage to women’s skin.

However heavy drinking can add a year to both sexes as can diabetes, chronic asthma or the regular use of painkillers.

Excessive exposure to sunlight had no effect on the perception of men’s ages but added over a year to women’s faces by the time they reached seventy.

Depression makes women look a lot older than men. Almost 4 extra years compared with 2.4 for men.

One of the researchers, Dr Kaare Christensen, said “It is a lot more dangerous looking one year older than one year younger”. “If you are not depressed, not lonely, not a smoker, and not too skinny, you are basically doing well”.

Dr Chris Philipson, professor of social gerontology at Keele University says “diet and exercise are crucial factors. You can do an awful lot over the age of 40 to 50 to change the way you experience growing old“.

Almost 90% of parents from the top two socio-economic groups are married in places such as Harrow or Wokingham according to a new marriage map produced by the Marriage Foundation.

They say “if our neighbours are married we are more likely to be married ourselves. In richer areas everyone across all social classes is more likely to be married, regardless of how well off they are“.

Across England and Wales the average marriage rate for people in socio-economic groups A & B is 79%.

Twenty council have higher proportions of married couples in these socio-economic groups.

Harrow – 88%

Wokingham – 87%

Surrey & West Berkshire – 86%

Buckinghamshire – 85%

Barnet – 85%

At the opposite end of the socio-economic scale the marriage rate in Liverpool and Knowsley among socio-economic groups D & E (manual and non-workers) is only 25%.

No more than 30% of parents with dependent children in the bottom 20 council areas were married. The average rate for marriage in these groups is 37%.

Liverpool & Knowsley – 25%

Salford, Blackpool, Wirral & Lambeth – 27

Experts believe that children from unmarried families have to contend with yet another factor which influences their life chances, inequality and social mobility.

A child born in 2017 has only a 50% chance of living with both parents by the time they reach fifteen. Of those parents who do stay together until their children reach fifteen, 93% are married.

And while there may not be a causal effect between being married and being rich if you don’t want your children to grow up poor you need to find a partner willing to work full-time according to Frank Field, a politician with a long interest in social inequality and fairness. Perhaps wealthier couples have more to lose if they split up so stay together longer regardless off how poor their relationship is. If you don’t have a lot to start with then you don’t have a lot to lose and you might be better off single and on benefits.

For years scientists have said that married people are happier, healthier and wealthier than single people.

Well it’s not true!

Single people exercise more, have better health and more friends compared to married people.

Psychologist Bella DePaulo says earlier studies are flawed because they didn’t take into account the consequences of divorce. In most studies people for whom marriage was awful were excluded as divorcees were counted as singletons.

In reality married people are unlikely to see life as a continuous opportunity to learn new things and develop friendships.

They are more likely to be putting up with an unfulfilling job and a dwindling circle of friends a they await their end.

DePaulo says that for many people being single is a positive, rational choice and they are living the dream.

Lifelong singletons also have more fulfilling jobs and are more interested in self-improvement.